KR101206597B1 - Process For The Working-Up Of Waste Waters Containing Aromatic Nitro Compounds - Google Patents

Abstract

The present invention relates to a process for treating crude wastewater produced during washing in an acidic washing process followed by an alkaline washing process, wherein the crude nitrobenzene prepared by thermally nitrifying benzene with nitrated acid. The alkaline wastewater to be treated generally contains benzene at a concentration of about 100 to about 3000 ppm and nitrobenzene at a concentration of about 1000 to about 10,000 ppm. In the process of the present invention, inexpensive benzene, nitrobenzene or mixtures thereof are separated from alkaline wastewater, and residual benzene, nitrobenzene or mixtures thereof are optionally stripped from alkaline wastewater, and benzene, nitrobenzene or The alkaline wastewater from which these mixtures have been removed is heated to a temperature of 150 ° C to 500 ° C under elevated pressure while blocking oxygen.

Adiabatic nitration of TPD process, alkaline wastewater, crude nitrobenzene, benzene

Description

Process For The Working-Up Of Waste Waters Containing Aromatic Nitro Compounds

Document 1 EP 0 005 203 A2 (BAYER AG) 1979.11.14

Document 2 EP 0 503 387 A1 (BASF AG) 1992.09.16

The present invention relates to a post-treatment method by thermal pressure decomposition (TPD) of alkaline wastewater produced upon washing of crude nitrobenzene.

The alkaline wastewater produced upon washing of crude nitrobenzene, in addition to water, generally contains not only nitrohydroxyaromatic compounds but also residual amounts of benzene and nitrobenzene. Examples of nitrohydroxyaromatic compounds which may be present in the form of water-soluble salts include mononitrophenol, dinitrophenol, trinitrophenol, mononitrocresol, dinitrocresol, trinitrocresol, mononitroresorcinol, dinitroresorcinol, trinitro Resorcinol, monoxyleneol, dixyleneol and trixyleneol. As the salt-forming agent, any metal capable of forming a water-soluble salt with a nitrohydroxyaromatic compound can be used. Alkali metals such as lithium, sodium, potassium and rubidium may be preferred.

Basic TPD methods for treating wastewater containing aromatic nitro compounds are described in EP 0 005 203 A2 and EP 0 503 387 A1. EP 0 005 203 A2 discloses a method for the post-treatment of waste water in which waste water containing nitrohydroxyaromatic compounds is treated at a pressure of 50 to 250 bar and a temperature of 150 to 500 ° C. while blocking air and oxygen.

EP 0 503 387 A1 describes a method similar to the above method, but post-treatment of alkaline wastewater by treatment at a temperature of 180 ° C. to 350 ° C. and a pressure of 40 to 250 bar after addition of nitric acid.

However, both methods have significant drawbacks.

EP 0 005 203 A2 makes no mention of removing organic hydrocarbons such as benzene or nitrobenzene obtained in the adiabatic nitration process corresponding to the state of the art. Therefore, the method for purifying wastewater according to the teaching of EP 0 005 203 A2 is inadequate and the consumption of sodium hydroxide solution used in the TPD process becomes very high.

In EP 0 503 387 A1, the decomposition of nitrobenzene is incomplete and requires further treatment of the waste water. Furthermore, the yield decreases as the nitrobenzene contained in the wastewater is decomposed in the TPD process. In addition, as required in accordance with the teaching of EP 0 503 387 A1, the use of nitric acid in a TPD process can lead to (1) consumption of nitric acid and (2) use of many materials in a titanium-lined tubular reactor. Process costs increase in some aspects, such as the burden and the associated high investment costs. Another disadvantage not mentioned in EP 0 503 387 is that the alkaline wastewater must be neutralized before the addition of nitric acid, which can optionally be carried out with an appropriate amount of nitric acid.

It is an object of the present invention to provide a simple and economical post-treatment method for alkaline wastewater produced upon washing of crude nitrobenzene prepared in the thermally insulating nitration process of benzene. It is also an object of the present invention to provide a method that has a low investment cost (ie no titanium-line device is required in the TPD process), low consumption of NaOH, and at the same time high purification efficiency.

These and other objects that will be apparent to those skilled in the art are achieved by separating benzene, nitrobenzene or mixtures thereof from alkaline wastewater and then heating the wastewater to a temperature of 150 ° C to 500 ° C while pressurizing in the absence of oxygen.

The present invention relates to a process for the workup of alkaline wastewater produced upon washing of crude nitrobenzene. The crude nitrobenzene to be washed is prepared by adiabatic nitration of benzene with nitrated acid. This crude nitrobenzene is first washed in an acidic washing process followed by an alkaline washing process. From this alkaline washing process, alkaline wastewater containing benzene at a concentration of about 100 to about 3000 ppm and nitrobenzene at a concentration of about 1000 to about 10,000 ppm is produced. Treated according to the process of the invention is such alkaline wastewater.

In the process of the present invention, insoluble benzene, nitrobenzene or mixtures thereof are separated from alkaline wastewater. The residual benzene, nitrobenzene or mixtures thereof are then stripped from the alkaline wastewater, which is then heated to a temperature of 150 ° C. to 500 ° C. under elevated pressure while blocking the oxygen with alkaline waste water from which benzene (nitrobenzene) has been removed. .

The nitration reaction of benzene to nitrobenzene is usually carried out by methods known to those skilled in the art, for example according to EP 0 436 443 A2.

The crude nitrobenzene is then washed in an acidic washing process. The concentration of acid used in this washing process is preferably adjusted to 0.5 to 2% by weight sulfuric acid based on the weight of the aqueous phase.

Crude nitrobenzene is subsequently washed in an alkaline washing process. The pH of the alkaline washing liquid is preferably adjusted to a value of 9 or more, most preferably to a value of 10 to 14. The alkaline wastewater resulting from this alkaline washing process is typically benzene at a concentration of about 100 to about 3000 ppm, preferably about 100 to about 1000 ppm and nitrobenzene at a concentration of about 1000 to about 10,000 ppm, preferably about 1200 to about 8,000 ppm. It contains. The wastewater also generally contains nitrohydroxyaromatic compounds at a concentration of about 2,000 to about 25,000 ppm. Post-treated by the process of the invention is alkaline wastewater produced from the alkaline wash liquor.

Inexpensive benzene, nitrobenzene or mixtures thereof remaining in the alkaline wastewater are separated from the wastewater. The separated benzene, nitrobenzene or mixtures thereof are then recycled to the nitrification process or recycled to crude nitrobenzene. Inexpensive nitrobenzene can be separated off by means of a separation device, a settling tank or any other known phase separation devices. Preference is given to using settling tanks. The alkaline wastewater remaining after separation of such inexpensive benzene, nitrobenzene or mixtures thereof preferably contains benzene at a concentration of about 100 to about 1,000 ppm and nitrobenzene at a concentration of about 1,200 to about 3,000 ppm.

Benzene and any residual nitrobenzene may then optionally be stripped from the alkaline wastewater. This is preferably done in a stripping column in which residual amounts of benzene and nitrobenzene are stripped off from the top by steam distillation. The vapor obtained containing benzene and nitrobenzene is then recycled, preferably to an alkaline washing process. The stripping column can be monitored for faults, for example by extra safety devices. The alkaline wastewater remaining after the stripping preferably contains only benzene at concentrations up to 10 ppm and nitrobenzene at concentrations up to 10 ppm.

The alkaline wastewater from which benzene, nitrobenzene or mixtures thereof are separated still contains organic salts of nitrohydroxyaromatic compounds. The wastewater is heated to a temperature of about 150 ° C to about 500 ° C, preferably about 250 ° C to about 350 ° C, most preferably about 270 ° C to about 290 ° C under elevated pressure, blocking oxygen. The wastewater may also be heated under inert gas pressure or under an inert gas permitting pressure of, for example, 0.1 to 100 bar. Examples of suitable inert gases are nitrogen, argon or mixtures thereof. Depending on the temperature and optionally the inert gas permitting pressure, the absolute pressure formed when the wastewater is heated is preferably from about 50 to about 350 bar, more preferably from about 50 to about 200 bar, most preferably from about 70 to about 130 bar range. Heating the alkaline wastewater and pyrolyzing the organic components present in the wastewater is generally carried out for about 5 to about 120 minutes, preferably about 15 to about 30 minutes.

The TPD plant section can be made of any sufficiently durable material, for example steel 1.4571. Sections in contact with the wastewater need not be coated with titanium. The wastewater treated according to the invention can preferably be discharged to, for example, a biological sewage treatment plant after passing through safety devices that control the phenolate content.

When optionally stripping benzene, nitrobenzene or mixtures thereof, benzene and nitrobenzene can be reduced to a content of up to 2 ppm by the process of the invention. If this stripping process is omitted, preferably a nitrobenzene content of up to 400 ppm, more preferably up to 200 ppm and a benzene content of preferably up to 10 ppm, more preferably up to 1 ppm can be obtained in the output of the TPD process. . The process of the present invention may also drop the content of nitrohydroxyaromatic compounds in the TPD process to less than 10 ppm, preferably less than 5 ppm.

In a preferred embodiment of the process of the present invention, a safety device is used to safeguard the concentration of aromatic compounds in alkaline wastewater before heating under pressure after separation of benzene, nitrobenzene or mixtures thereof to remove potentially explosive hazards in the TPD process. Managed by It preferably monitors the phase interface in the alkaline washing process (monitoring whether the drained water phase is essentially free of organic moieties), monitors the phase interface in the separation process of benzene and nitrobenzene, and pH, density, or both Is also monitored by heating the wastewater under pressure and optionally monitoring with a FID (flame ionization detector).

The alkaline wastewater produced upon washing of crude nitrobenzene may also be mixed with wastewater containing aniline and aminohydroxyaromatic compounds obtained, for example, in the preparation of aniline. Such wastewater obtained from the aniline preparation process preferably contains aliphatic and aromatic hydrocarbons at a concentration of 1 to 10 ppm and phenol and phenolic salts at a concentration of about 200 to about 1500 ppm.

The process according to the invention is advantageous in that it is possible to reduce the consumption of NaOH during the heating step under pressure by removing significant amounts of benzene, nitrobenzene or mixtures thereof. Thus, the method of the present invention minimizes the consumption of NaOH and the extent to which benzene and nitrobenzene are degraded and lost in the TPD process. The direct advantage of using lower amounts of NaOH is that there is no need to use a high level of internal plant material to construct the plant section of the TPD process. As the pre-separation of benzene and nitrobenzene results in fewer overall organic components to be reduced in the TPD process, the production capacity of the TPD process is ultimately increased and in this way the purity of the post-treated wastewater is improved. Thus, the wastewater treated by the method according to the invention can be discharged directly to the biological sewage treatment plant without dilution.

The invention is illustrated in detail in the following examples, which are provided to illustrate the invention.

Example

Example 1 (comparative example from EP 0 005 203 A2)

1200 ml of aqueous-alkaline wastewater obtained from the adiabatic nitration process was introduced into a nitrogen-flushed 2 L autoclave equipped with a stirrer, pressure gauge and thermometer. Nitrogen was then charged under a pressure of 30 bar. The wastewater was then heated to 300 ° C. and maintained at a reaction temperature of 300 ° C. for 15 minutes (TPD process). The pressure was raised to 114 bar. After cooling, the wastewater was recovered and analyzed. Table 1 below shows the analytical values for the contents of various organic materials before and after TPD.

Example 2 (comparative example from EP 0 503 387 A1)

Wastewater having the composition shown in Table 2 below was treated in a tubular reactor under the following reaction conditions:

Reaction temperature: 280 ° C to 290 ° C

Pressure: 95bar

Addition amount of nitric acid: 1.5% by weight based on the weight of waste water

Retention time: 5 minutes

The analysis results before and after the treatment of the wastewater are shown in Table 2 below.

Example 3 (Example according to the present invention)

The crude nitrobenzene obtained from the adiabatic nitration of benzene was first washed in an acidic washing process and then under alkaline conditions with the addition of sodium hydroxide solution (50%) in a stirred tank. The mixture was then separated into an organic phase (crude nitrobenzene) and an aqueous phase (alkaline wastewater, waste liquor) in the first downstream separation tank based on its density difference. Nitrobenzene was saturated in alkaline wastewater, and the wastewater had the composition shown in Table 3 below. This was then passed through another separation tank, in which nitrobenzene and benzene were unsustained at the bottom and separated out by phase separation. The alkaline wastewater obtained from the separation tank was mixed with the wastewater obtained from the workup of aniline and further subjected to TPD treatment. Table 3 below shows the analytical data on the composition of the alkaline wastewater before the first separation tank, after the first separation tank (after mixing with the wastewater obtained from the post-treatment of aniline) and after TPD.

The TPD process was performed at 100 bar and 290 ° C. with a residence time of 30 minutes and a narrow residence time distribution.

Example 4 (Example according to the invention)

The crude nitrobenzene obtained from the adiabatic nitration of benzene was first washed in an acidic washing process and then under alkaline conditions with the addition of sodium hydroxide solution (32%) in a stirred tank. The mixture was then separated into an organic phase (crude nitrobenzene) and an aqueous phase (alkaline wastewater, waste liquor) based on its density difference in the first downstream separation tank. Nitrobenzene was saturated in alkaline wastewater, and the wastewater had the composition shown in Table 4 below. This was then passed through another separation tank, in which nitrobenzene and benzene were unsustained at the bottom and separated out by phase separation. The waste liquor was then fed to a stripping column operated with live steam where nitrobenzene and benzene were stripped off overhead. The alkaline wastewater obtained from the bottom of the column had the composition shown in Table 4 below and was further worked up by TPD and then some streams were analytically monitored using FID for the presence of nitrobenzene and benzene.

The TPD process was performed at 110 bar and 275 ° C. with a residence time of 30 minutes and a narrow residence time distribution. After the TPD process, the wastewater had the composition shown in Table 4 above and could be discharged directly to the biological sewage treatment plant.

Although described in detail above to illustrate the invention, this description has been made by the person skilled in the art without departing from the spirit and scope of the invention, except that it is made for illustrative purposes only and may be limited by the following claims. It should be understood that this can be done.

According to the method of the present invention, alkaline wastewater generated during washing of crude nitrobenzene can be post-treated at a high investment efficiency while using a small amount of NaOH at a low investment cost.

Claims (5)

Crude nitrobenzene obtained by adiabatic nitration of benzene with nitric acid is a method for treating alkaline wastewater containing 100 to 3000 ppm benzene and 1000 to 10,000 ppm nitrobenzene generated when the acid is washed with an alkaline substance. , (a) isolating benzene, nitrobenzene or mixtures thereof from alkaline wastewater; (b) stripping residual benzene, nitrobenzene or mixtures thereof from the alkaline wastewater from step (a); And (c) heating the alkaline wastewater from step (a) or (b) to a temperature of 150 ° C to 500 ° C while pressurizing in the absence of oxygen A method of treating alkaline wastewater, including. The process of claim 1 wherein in step (b) residual benzene, nitrobenzene or mixtures thereof are stripped from the wastewater using steam. The method of claim 1 wherein step (c) is performed at an absolute pressure of 50 to 350 bar. The process of claim 2 wherein step (c) is carried out at an absolute pressure of 50 to 350 bar. The process according to claim 1, wherein the alkaline wastewater from which benzene, nitrobenzene or mixtures thereof are separated, stripped, or separated and stripped is combined with wastewater containing aniline, aminohydroxyaromatic compounds or mixtures thereof, followed by step (c How to do it.